barm,
That information was in Jim Carmichel's BOOK OF THE RIFLE, and I've quoted it here and there. But I would assume Ruger was testing with factory ammo, and there may have been something about the ammo that affected results.
My own .22-250's and Swifts, all factory rifles of various kinds, haven't shown any clear pattern either way. I would guess really well-made rifles in both chamberings would shoot well, since most of my factory rifles have shot well--but would also assume the .22-250 would have a slight edge in custom rifles, if somebody did enough shooting in enough rifles.
Might have to ask some bullet companies what their results are with both cartridges when shooting on their indoor ranges.
